Analysis of human acetylation stoichiometry defines mechanistic constraints on protein regulation

Lysine acetylation is a reversible posttranslational modification that occurs at thousands of sites on human proteins. However, the stoichiometry of acetylation remains poorly characterized, and is important for understanding acetylation-dependent mechanisms of protein regulation. Here we provide accurate, validated measurements of acetylation stoichiometry at 6,829 sites on 2,535 proteins in human cervical cancer (HeLa) cells. Most acetylation occurs at very low stoichiometry (median 0.02%), whereas high stoichiometry acetylation occurs on nuclear proteins involved in gene transcription and on acetyltransferases. Analysis of acetylation copy number shows that histones harbor the majority of acetylated lysine residues in human cells. Class I deacetylases target a greater proportion of high stoichiometry acetylation compared to SIRT1 and HDAC6. The acetyltransferases CBP and p300 catalyze a majority (65%) of high stoichiometry acetylation, yet also target sites with low stoichiometry. This resource dataset provides valuable information for understanding the impact of individual acetylation sites on protein function.